High-power field-effect transistor (FET) switches are commonly used in radio-frequency/microwave circuits in wireless communications and radar systems. For high-power switching, FET switches are often either biased or include shunt devices for providing isolation of signal paths. Although these shunt devices provide isolation, the shunt devices also tend to increase circuit complexity, die-area consumption, and cost.
Refer, for example, to the switch 100 and a self-biasing shunt device 102 illustrated in FIG. 1. The shunt device 102 includes an active device 104 having a DC-blocked source terminal 106 and a DC-blocked drain terminal 108. The DC blocking is provided by a first capacitor 110 and a second capacitor 112, respectively. The drain terminal 108 of the active device 104 is coupled to the source of the last active device 126 of the series-stacked FETs on the signal path 114 between the antenna terminal 116 and the transmit/receive terminal 118. The drain terminal 108 of the active device 104 is also coupled by way of a resistor 120 to a control line 122 coupled to the control terminal 124.
In this configuration, two capacitors are required for DC-blocking the active device 104 of the shunt device 102. Not only do capacitors tend to be relatively large (compared to other passive devices, for example), but capacitors can also tend to be sensitive to electrostatic discharge.